Photoelectric conversion device, method of manufacturing the same, and camera

ABSTRACT

A photoelectric conversion device has a silicon substrate which includes a first portion configured to perform photoelectric conversion, and a second portion which is arranged farther apart from a light receiving surface of the silicon substrate than the first portion and contains carbon. A first peak concentration as a carbon peak concentration in the second portion is not less than 1×10 18  [atoms/cm 3 ] and not more than 1×10 20  [atoms/cm 3 ], and a second peak concentration as an oxygen peak concentration in the second portion is not less than 1/1000 and not more than 1/10 of the first peak concentration.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a photoelectric conversion device, amethod of manufacturing the same, and a camera.

Description of the Related Art

If a metal impurity is mixed into a pixel portion in the manufacturingprocess of a solid-state image sensor, an increase in dark current of aphotoelectric conversion element and occurrence of a white defect arecaused. Mixture of the metal impurity into the pixel portion can becaused not only by a manufacturing apparatus but also by thermaldiffusion of a silicide material used for a peripheral circuit portion.Japanese Patent Laid-Open No. 10-41311 is related to a getteringtechnique in a solid-state image sensing element. Japanese PatentLaid-Open No. 10-41311 describes obtaining a gettering capability byion-implanting carbon and oxygen in a silicon substrate. Japanese PatentLaid-Open No. 10-41311 also describes that it is desirable that anoxygen peak concentration is set equal to or higher than a carbon peakconcentration, and oxygen and carbon are made equal to each other inprojection range after ion implantation in order to obtain a stronggettering capability by effectively forming a compound of oxygen andcarbon.

However, if oxygen is implanted in the silicon substrate intentionally,oxygen that diffuses into an epitaxial layer in an annealing process orthe like during the manufacturing process increases. This may induce acrystal defect owing to oxygen in a region close to a pixel. Inparticular, when a metal such as Co or Ni whose diffusion rate is highin silicon in a low temperature is used, it is desirable that thecrystal defect in the epitaxial layer close to the pixel is suppressed,and the metal is captured in a gettering layer formed in the region asdeep as possible.

If an oxygen concentration in the silicon substrate is high, or ifoxygen is ion-implanted intentionally in the silicon substrate, it isconsidered that not the metal to be captured but oxygen is gettered in alarge amount due to a distortion caused by arranging carbon at thelattice position of silicon. This means that the effect of gettering themetal decreases. For the above-described reasons, it cannot be said thatthe conventional gettering technique is optimal as a method of reducinga white defect failure of the solid-state image sensor.

SUMMARY OF THE INVENTION

The present invention provides a technique advantageous in suppressingoccurrence of a white defect.

One of aspect of the present invention provides a photoelectricconversion device that includes a silicon substrate, wherein the siliconsubstrate includes a first portion configured to perform photoelectricconversion, and a second portion which is arranged farther apart from alight receiving surface of the silicon substrate than the first portionand contains carbon, a first peak concentration as a carbon peakconcentration in the second portion is not less than 1×10¹⁸ [atoms/cm³]and not more than 1×10²⁰ [atoms/cm³], and a second peak concentration asan oxygen peak concentration in the second portion is not less than1/1000 and not more than 1/10 of the first peak concentration.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically showing the partial arrangementof a solid-state image sensor according to the first embodiment of thepresent invention;

FIG. 2 is a view for explaining a method of manufacturing thesolid-state image sensor according to the first embodiment of thepresent invention;

FIG. 3 is a graph showing the concentrations of carbon (impurity) andoxygen in an example of the solid-state image sensor according to thefirst embodiment of the present invention;

FIG. 4 is a graph showing the concentrations of carbon (impurity) andoxygen in a solid-state image sensor according to a comparative example;

FIG. 5 is a graph plotting the number of white defects in a solid-stateimage sensor, and an index (oxygen peak concentration/carbon peakconcentration) obtained by measuring a semiconductor substrate in thesolid-state image sensor according to the example and a comparativeexample;

FIG. 6A is a graph obtained by rewriting the abscissa of FIG. 5 into arange of 0% to 120%;

FIG. 6B is a graph plotting two data of FIG. 3 in Japanese PatentLaid-Open No. 10-41311;

FIG. 7 is a graph showing the concentration distribution of cobalt (Co)near the surface of a pixel region (photoelectric converter PD) in asolid-state image sensor according to each of the example, ComparativeExample 1, and Comparative Example 2 of the present invention;

FIG. 8 is a graph showing the number of white defects in a solid-stateimage sensor according to each of the example, Comparative Example 4,Comparative Example 5, and Comparative Example 6 of the presentinvention;

FIG. 9 is a sectional view schematically showing the partial arrangementof a solid-state image sensor according to the second embodiment of thepresent invention;

FIG. 10 is a graph showing the concentration of an impurity of thesecond conductivity type (p type), the concentration of oxygen, and theconcentration of an impurity (carbon) taken along a line A-A′ in FIG. 9;

FIG. 11 is a sectional view for explaining a solid-state image sensorand a method of manufacturing the same according to the third embodimentof the present invention;

FIG. 12 is a sectional view for explaining the solid-state image sensorand the method of manufacturing the same according to the thirdembodiment of the present invention; and

FIG. 13 is a block diagram showing the arrangement of a camera accordingto an embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

The present invention will now be described with reference to theaccompanying drawings by way of exemplary embodiments. A photoelectricconversion device of the present invention can be formed as, forexample, a solid-state image sensor, phase difference detection device,light amount sensor, or the like that detects one-dimensional ortwo-dimensional image information. The solid-state image sensor may beformed as a MOS image sensor, a CCD image sensor, or an image sensor ofany other type. An example will be described below in which thephotoelectric conversion device of the present invention is applied tothe MOS image sensor (solid-state image sensor). However, this does notintend to limit the present invention to the MOS image sensor.

FIG. 1 shows the partial arrangement of a solid-state image sensor 100according to the first embodiment of the present invention. Thesolid-state image sensor 100 has a semiconductor substrate SS (siliconsubstrate) including a first semiconductor region 101 and a secondsemiconductor region 102 arranged on the first semiconductor region 101.The first semiconductor region 101 includes an impurity-containingportion 190. The semiconductor substrate SS has a first surface S1 and asecond surface S2 which are surfaces on opposite sides. One of twosurfaces of the second semiconductor region 102 opposite to the firstsemiconductor region 101 forms the first surface S1 of the semiconductorsubstrate SS. One of two surfaces of the first semiconductor region 101opposite to the second semiconductor region 102 forms the second surfaceS2 of the semiconductor substrate SS. The second semiconductor region102 continues from the first semiconductor region 101. That is, noinsulator region exists between the first semiconductor region 101 andthe second semiconductor region 102.

In this example, both the first semiconductor region 101 and the secondsemiconductor region 102 have the first conductivity type. That is, inthis example, the first semiconductor region 101 and the secondsemiconductor region 102 have the same conductivity type. The firstsemiconductor region 101 and the second semiconductor region 102 mayhave different conductivity types. A plurality of impurity regions whoseconductivity types or impurity concentrations are different from eachother are provided in the second semiconductor region 102, as will bedescribed later.

Note that in a description below, the conductivity type of asemiconductor region (impurity region) that makes charges of the sametype as signal charges form a majority carrier and makes charges of adifferent type from the signal charges form a minority carrier will bereferred to as the first conductivity type. Then, the conductivity typeof a semiconductor region (impurity region) that makes charges of adifferent type form the signal charges form a majority carrier and makescharges of the same type as the signal charges form a minority carrierwill be referred to as the second conductivity type. For example, ifelectrons are the signal charges, the first conductivity type is an ntype, and the second conductivity type is a p type.

The concentration of an impurity of the first conductivity type in thefirst semiconductor region 101 is different from the concentration of animpurity of the first conductivity type in the second semiconductorregion 102. In one example, the concentration of the impurity of thefirst conductivity type in the first semiconductor region 101 is higherthan the concentration of the impurity of the first conductivity type inthe second semiconductor region 102. In another example, theconcentration of the impurity of the first conductivity type in thefirst semiconductor region 101 is lower than the concentration of theimpurity of the first conductivity type in the second semiconductorregion 102.

The first semiconductor region 101 can be formed by a single crystalsilicon wafer (silicon plate). More specifically, the firstsemiconductor region 101 can be formed by a single crystal silicon waferformed by slicing a single crystal silicon ingot and polishing theslice. The second semiconductor region 102 is made of single crystalsilicon, and can be formed by epitaxially growing a single crystalsilicon layer on the first semiconductor region 101. The single crystalsilicon layer formed by epitaxial growth is called an epitaxial layer.Since a crystal lattice can continue between the first semiconductorregion 101 and the second semiconductor region 102, it may be impossibleto observe a clear interface.

The semiconductor substrate SS that forms the solid-state image sensor100 can include a photoelectric converter PD as the first portion whichperforms photoelectric conversion, and the impurity-containing portion190 as the second portion which is arranged farther apart from the lightreceiving surface of the semiconductor substrate SS than thephotoelectric converter PD and contains a group 14 element other thansilicon. The impurity-containing portion 190 (second portion) containsthe group 14 element (impurity) other than silicon (Si) and oxygen (O).Note that the group 14 element includes carbon (C), silicon (Si),germanium (Ge), tin (Sn), and lead (Pb). Carbon (C) smaller in atomicnumber than silicon (Si) is preferable as the group 14 element otherthan silicon. The first peak concentration as a peak concentration ofthe group 14 element other than silicon in the impurity-containingportion 190 (second portion) can be 1×10¹⁸ [atoms/cm³] or more and1×10²⁰ [atoms/cm³] or less. The second peak concentration as an oxygenpeak concentration in the impurity-containing portion 190 (secondportion) can be 1/1000 or more and 1/10 or less of the first peakconcentration (the peak concentration of 1×10¹⁸ [atoms/cm³] or more and1×10²⁰ [atoms/cm³] or less). The solid-state image sensor 100manufactured by using the above-described semiconductor substrate SS isadvantageous in reducing white spots. The solid-state image sensor 100manufactured by using the above-described semiconductor substrate SS isalso advantageous in reducing afterimages in the photoelectric converterPD.

Light enters the photoelectric converter PD via the first surface S1.The impurity-containing portion 190 is arranged apart from the lightreceiving surface of the semiconductor substrate SS. The light receivingsurface can be defined as a portion of the first surface S1 of thesemiconductor substrate SS positioned above the photoelectric converterPD. The impurity-containing portion 190 can be arranged in isolationfrom the photoelectric converter PD. However, a distance between theimpurity-containing portion 190 and the photoelectric converter PD canbe less than 20 μm. The photoelectric converter PD (first portion) canbe arranged between the impurity-containing portion 190 (second portion)and the light receiving surface (first surface S1) in a directionperpendicular to the light receiving surface. The impurity-containingportion 190 can be arranged so as to form a layer parallel to the firstsurface S1. The impurity-containing portion 190 can be arranged suchthat a depth from the first surface S1 (a distance from the lightreceiving surface) falls within a range of 3 μm to 20 μm. In oneexample, the impurity-containing portion 190 includes a region (firstregion) with the concentration of an impurity (the group 14 elementother than silicon) being 1×10¹⁸ [atoms/cm³] or more, and the dimensionof the region in the direction perpendicular to the first surface S1(light receiving surface) can be 3 μm or less.

In this example, the impurity-containing portion 190 is arranged in thefirst semiconductor region 101. However, the impurity-containing portion190 may be arranged in, for example, an impurity region 102 a. Thephotoelectric converter PD is arranged in at least the secondsemiconductor region 102. In this example, the photoelectric converterPD is arranged in the second semiconductor region 102. However, thephotoelectric converter PD can be extended to the first semiconductorregion 101. The photoelectric converter PD includes an impurity region104 of the first conductivity type capable of functioning as a chargeaccumulation region. In the impurity region 104 of the firstconductivity type, signal charges form the majority carrier. Thephotoelectric converter PD can also include, between the impurity region104 and the first semiconductor region 101, an impurity region 103having the second conductivity type different from the firstconductivity type. The photoelectric converter PD can also include,under the impurity region 104, an impurity region 102 b of the firstconductivity type arranged continuously from the impurity region 104. Aportion arranged under the impurity region 103 out of the secondsemiconductor region 102 is the impurity region 102 a. A portionarranged on the impurity region 103 out of the second semiconductorregion 102 is the impurity region 102 b.

The concentration of the impurity of the first conductivity type in theimpurity region 104 is higher than the concentration of the impurity inthe second semiconductor region 102 (the impurity regions 102 a and 102b). The impurity regions 104, 102 b, and 103 form the photoelectricconverter PD. Out of negative charges (electrons) and positive charges(holes) generated by photoelectric conversion of the photoelectricconverter PD, charges of the same type as the majority carrier in thefirst conductivity type are accumulated in the impurity region 104. Thephotoelectric converter PD can include an impurity region 105 having thesecond conductivity type and arranged on the upper side of the impurityregion 104, that is, between the impurity region 104 and the surface ofthe semiconductor substrate SS. The impurity region 105 functions toisolate the impurity region 104 from the surface of the semiconductorsubstrate SS. The photoelectric converter PD having a buried photodiodestructure is thus formed.

Although not illustrated, the solid-state image sensor 100 includes aplurality of impurity regions 104. The plurality of impurity regions 104can be isolated from each other by impurity regions 106 and 107 of thesecond conductivity type each functioning as an isolation region basedon a potential barrier. The impurity region 103 can be arranged underthe array of the plurality of impurity regions 104 so as to spreadthroughout the region of the array. The solid-state image sensor 100includes a plurality of pixels. Each pixel includes the photoelectricconverter PD including the impurity region 104.

Charges accumulated in the impurity region 104 of the photoelectricconverter PD are transferred to an impurity region 112 of the firstconductivity type functioning as a floating diffusion region via achannel that is formed in the impurity region 102 b when a potential ofactive level is applied to a gate electrode 114. The impurity region 112is formed between the surface of the semiconductor substrate SS and theimpurity region 102 b out of the second semiconductor region 102. Thegate electrode 114 is arranged on a gate insulating film 116 on thesemiconductor substrate SS. The impurity regions 104 and 112, the gateelectrode 114, and the gate insulating film 116 have a MOS transistorstructure. An impurity region 111 functioning as a field relaxationregion can be arranged so as to be adjacent to the impurity region 112on a side of the impurity region 112 close to the impurity region 104.The impurity region 111 can have the first conductivity type.

The solid-state image sensor 100 can include a plurality of transistorsTr to output, to a column signal line, a signal corresponding to thecharges transferred to the impurity region 112. The plurality oftransistors Tr are arranged on the surface side of the semiconductorsubstrate SS. Each transistor Tr can include impurity regions 113 thatform a source and a drain, a gate electrode 115, and a gate insulatingfilm 117. Out of elements including the plurality of transistors Tr andimpurity regions 104 (photoelectric conversion elements), elements to beisolated can be isolated by an element isolation portion 110. Theelement isolation portion 110 can be formed by an insulator having anSTI structure or LOCOS structure formed on the surface side of thesemiconductor substrate SS. However, the element isolation portion 110can also be formed by a p-n junction isolation. An impurity region 109of the second conductivity type is formed around the element isolationportion 110. The impurity region 109 can function as a channel stop or ashield to a dark current generated in the interface between the elementisolation portion 110 and the second semiconductor region 102. Animpurity region 108 having the second conductivity type can be arrangedbetween the impurity region 109 and the impurity region 103.

Although not shown in FIG. 1, the solid-state image sensor 100 caninclude a pixel portion that includes a plurality of pixels eachincluding the photoelectric converter PD and a peripheral circuitportion configured to read out signals from the pixels of the pixelportion. The plurality of pixels can be arrayed in the pixel portion soas to form a plurality of rows and a plurality of columns. Theperipheral circuit portion can include, for example, a row selectingcircuit that selects the rows in the pixel portion, a signal readoutcircuit that reads out signals from the pixels of each column in thepixel portion, a column selecting circuit that selects the columns inthe pixel portion, and the like. The peripheral circuit portion caninclude a transistor including a silicide region formed by silicide as acompound of a metal and silicon (a constituent material for thesemiconductor substrate SS or a constituent material for the gateelectrode). The metal that forms silicide can contain at least one of,for example, nickel, cobalt, titanium, molybdenum, and tungsten.

An insulating layer 118, a plurality of insulating layers 123, wiringlayers 120 and 122, a contact plug 119, a via plug 121, and the like canbe arranged on the semiconductor substrate SS. The insulating layer 118can function as, for example, an antireflection film and/or an etchingstopper. The plurality of insulating layers 123 can function asinterlayer dielectric films. A color filter layer 124, a microlens 125,and the like can be arranged on the plurality of insulating layers 123.

A method of manufacturing the solid-state image sensor 100 of the firstembodiment will be described below with reference to FIG. 2. First, instep S200, a single crystal silicon substrate as the first semiconductorregion 101 is prepared by mirror-polishing and cleaning a wafer that issliced from a single crystal silicon ingot pulled by an MCZ method. Notethat oxygen is mixed into silicon while fabricating the ingot. It ispossible, however, to control an oxygen concentration in the ingot(resulting first semiconductor region 101) by adjusting a condition suchas a rotation speed, applied magnetic field, atmosphere, or the like inpulling. With this adjustment, the oxygen concentration in the ingot(resulting first semiconductor region 101) is controlled to fall withina range of 2×10¹⁶ [atoms/cm³] or more to 8×10¹⁷ [atoms/cm³], forexample, at 5×10¹⁷ [atoms/cm³]. The oxygen concentration can be obtainedfrom a conversion factor by Old ASTM.

When the first semiconductor region 101 having the oxygen concentrationof 8×10¹⁷ [atoms/cm³] or less is used, it is possible to suppress theconcentration of oxygen captured in the impurity-containing portion 190to 1/10 or less of the concentration of the group 14 element other thansilicon in the manufactured solid-state image sensor 100. On the otherhand, when the first semiconductor region 101 (single crystal siliconsubstrate) having the oxygen concentration of 2×10¹⁶ [atoms/cm³] or lessis used, a mechanical strength may be decreased, and a yield in themanufacturing process of the solid-state image sensor 100 may bedecreased. Note that the dimension (diameter), resistivity, conductivitytype, and the like of the first semiconductor region 101 (single crystalsilicon substrate) are not particularly limited.

Then, in step S210, an ion implanter is used to accelerate and implant,for example, carbon ions as the group 14 element (impurity) other thansilicon in the first semiconductor region 101 (single crystal siliconsubstrate). Consequently, the impurity-containing portion 190 is formedin the first semiconductor region 101. Carbon implantation can beperformed by an ion implantation method of ionizing and implantingcarbon. The impurity-containing portion 190 may be formed in thevicinity of the surface of the first semiconductor region 101 or may beformed inside the first semiconductor region 101. Note that in place ofcarbon, a hydrocarbon molecule that contains carbon may be adopted as animpurity. The purpose of ion implantation is to create a localdistortion in silicon by introducing an element which belongs to thesame group (group 14) as silicon and different in atomic radius fromsilicon. Hence, not carbon but germanium, tin, or lead may be implantedin the first semiconductor region 101 (single crystal silicon substrate)as an impurity.

An acceleration energy at the time of ion implantation of the impuritycan fall within a range of, for example, 10 KeV to 200 KeV. Animplantation dose at the time of ion implantation of the impurity canfall within a range of, for example, 1×10¹⁴ [atoms/cm²] to 5×10¹⁵[atoms/cm²]. Note that if the dose is too low, a gettering effect to bedescribed later decreases. On the other hand, if the dose is too high,the second semiconductor region 102 (epitaxial layer) may be formed onthe first semiconductor region 101 which has a crystal defect caused byion implantation, resulting in forming a crystal defect in the secondsemiconductor region 102. An impurity dose can be decided such that theconcentration of oxygen captured in the impurity-containing portion 190(gettering layer) becomes 1/10 or less of the concentration of the group14 element (impurity) other than silicon in the manufactured solid-stateimage sensor 100.

On the other hand, if the impurity dose is 5×10¹⁵ [atoms/cm²], and animpurity peak concentration is 10×10¹⁹ [atoms/cm³], the oxygen peakconcentration is desirably higher than 1×10¹⁷ [atoms/cm³]. This isbecause the crystal defect in the second semiconductor region 102 or adecrease in mechanical strength of the first semiconductor region 101caused by a low oxygen concentration may occur if the oxygen peakconcentration becomes 1×10¹⁷ [atoms/cm³] or less. It is thereforedesirable that the peak oxygen concentration in the impurity-containingportion 190 is made 1/1000 or more of the impurity peak concentration inthe impurity-containing portion 190.

In one example, an arrangement can be adopted in which the oxygenconcentration is 2×10¹⁷ [atoms/cm³] or less in a portion where thephotoelectric converter PD is provided, and the oxygen peakconcentration is 2×10¹⁸ [atoms/cm³] or more in a portion deeper than thephotoelectric converter PD.

Then, in step S220, the second semiconductor region 102 (epitaxiallayer) is formed by epitaxial growth on a surface where the impurity(carbon) of the first semiconductor region 101 (single crystal siliconsubstrate) is ion-implanted. In one example, the thickness of the secondsemiconductor region 102 is 9 μm.

The element isolation portion 110, the impurity regions 103, 108, and109, the photoelectric converter PD, the impurity regions 111, 112, and113, and the like can be formed in the semiconductor substrate SS below.The gate electrodes 114 and 115, the gate insulating films 116 and 117,the insulating layers 118 and 123, the wiring layers 120 and 122, thecontact plug 119, the via plug 121, the color filter layer 124, themicrolens 125, and the like can also be formed on the semiconductorsubstrate SS.

In the above-described manufacturing process, the semiconductorsubstrate SS undergoes annealing in order to, for example, form an oxidefilm, activate an impurity, or the like. The maximum temperature in thisannealing is typically about 900° C. to 1,100° C. In the process of thisannealing, silicon in the semiconductor substrate SS (firstsemiconductor region 101) is substituted by the impurity such as carbon,and this may cause a local distortion. As a result, theimpurity-containing portion 190 functions as a gettering portion or agettering layer that captures heavy metals such as cobalt and nickel.

In one example, in the manufactured solid-state image sensor 100, theimpurity-containing portion 190 includes a region (second region) withan impurity concentration of 1×10¹⁹ [atoms/cm³] or more, and an oxygenconcentration in the region is 3×10¹⁸ [atoms/cm³] or less. Note that theregion with the impurity concentration of 1×10¹⁹ [atoms/cm³] or more hasa distortion caused by substituting silicon with the impurity, and thisdistortion can capture the heavy metals such as cobalt and nickel inaddition to oxygen. The fact that the oxygen concentration in the regionis 3×10¹⁸ [atoms/cm³] or less means that the region has a sufficientcapability to capture the heavy metals, that is, a sufficient getteringcapability.

FIG. 3 shows the concentrations of carbon (impurity) and oxygen in asolid-state image sensor according to an example of the presentinvention. FIG. 4 shows the concentrations of carbon (impurity) andoxygen in a solid-state image sensor according to a comparative example.Note that in the example, a first semiconductor region 101 (singlecrystal silicon substrate) with an oxygen concentration of 5×10¹⁷[atoms/cm³] is prepared in step S200. On the other hand, in thecomparative example, a first semiconductor region 101 (single crystalsilicon substrate) with an oxygen concentration of 1.3×10¹⁸ [atoms/cm³]is prepared in step S200. Other conditions are the same in the exampleand the comparative example. In FIGS. 3 and 4, the abscissa indicatesthe depth from a first surface S1 of a semiconductor substrate SS.Measurement of the concentrations of carbon and oxygen is performed bySIMS analysis.

From the results of FIGS. 3 and 4, oxygen also exists at a highconcentration in a region (impurity-containing portion) where carbon asthe impurity is implanted. In addition, in FIGS. 3 and 4, distributionshapes of carbon and oxygen are similar to each other. It is estimatedfrom this that oxygen present between silicon lattices gathers in adistortion caused by carbon. In the example shown in FIG. 3, the firstsemiconductor region 101 (single crystal silicon substrate) lower inoxygen concentration than the comparative example is used, and thus theamount of oxygen in the region (impurity-containing portion) wherecarbon is implanted is smaller than in the comparative example in themanufactured solid-state image sensor. As shown in FIGS. 3 and 4, a peakvalue in an oxygen concentration distribution (to be referred to as anoxygen concentration peak hereinafter) and a peak value in a carbonconcentration distribution (to be referred to as a carbon concentrationpeak) almost match in depth. Therefore, a value obtained by dividing theoxygen peak concentration by the carbon peak concentration is calculatedand used as an index of the oxygen concentration in theimpurity-containing portion serving as a gettering layer.

FIG. 5 is a graph plotting the number of white defects in thesolid-state image sensor and an index (oxygen peak concentration/carbonpeak concentration) obtained by measuring the semiconductor substrate SSin the solid-state image sensor according to the example and thecomparative example. The number of white defects of the ordinate is avalue obtained by operating the solid-state image sensor under a darkenvironment for a short time and counting the number of pixels eachindicating a specific high output value as the number of white detects.As is apparent from FIG. 5, it can be seen that the number of whitedefects decreases as compared with the comparative example if the oxygenconcentration is 1/10 or less (10.0% or less) of the concentration ofcarbon as the impurity.

FIG. 3 in Japanese Patent Laid-Open No. 10-41311 shows that the numberof white defects decreases as an oxygen dose increases. On the otherhand, the present inventor found that it is possible to decrease thenumber of white defects by manufacturing a solid-state image sensor 100such that an oxygen concentration in an impurity-containing portion 190becomes 1/10 or less of the impurity concentration in theimpurity-containing portion 190 as described above. Both may seem tocontradict, and thus this will be described.

FIG. 6A is a graph obtained by rewiring the abscissa of FIG. 5 into arange of 0% to 120%. FIG. 6B is a graph plotting two data of FIG. 3 inJapanese Patent Laid-Open No. 10-41311. One data is obtained when carbondose=5×10¹⁴ [atoms/cm⁻²], and oxygen dose=5×10¹⁴ [atoms/cm⁻²]. The otherdata is obtained when carbon dose=5×10¹⁴ [atoms/cm⁻²], and oxygen dose=0[atoms/cm⁻²]. Note that assuming a substrate having a general oxygenconcentration, oxygen peak concentration/carbon peak concentration whenoxygen dose=0 [atoms/cm⁻²] is set at 20%. In Japanese Patent Laid-OpenNo. 10-41311, focus is placed not on the oxygen concentration in thesubstrate but on the oxygen dose with respect to the substrate. Inpractice, a general single crystal silicon substrate contains thesubstantial amount of oxygen, and Japanese Patent Laid-Open No. 10-41311does not consider this. As can be seen from FIGS. 6A and 6B, the exampleof the present invention is superior to data described in JapanesePatent Laid-Open No. 10-41311, and then the present invention specifiesa parameter which is not assumed in Japanese Patent Laid-Open No.10-41311.

In a range with a high oxygen concentration, many oxygen precipitationdefects are formed not only in the first semiconductor region 101 butalso in a second semiconductor region 102 (epitaxial layer), and thusmany places each capable of capturing a metal impurity exist other thanin the impurity-containing portion 190 where an impurity is implanted.It is therefore estimated that in the range with the high oxygenconcentration, the number of white defects decreases by increasing theoxygen precipitation defects. It is estimated, however, that an effectof decreasing the number of white defects by increasing the oxygenprecipitation defects is limited. In order to further decrease thenumber of white defects, the oxygen precipitation defects rather becomeobstacles, and capturing a metal by a distortion formed by the impurityin the impurity-containing portion 190 is considered more effective.That is, in order to further decrease the number of white defects,controlling the oxygen concentration such that the oxygen concentrationin the impurity-containing portion 190 becomes 1/10 or less of theimpurity concentration in the impurity-containing portion 190 in thecompleted solid-state image sensor 100 is considered effective. Ifoxygen is captured by the distortion formed by the impurity in theimpurity-containing portion 190, the capability of the distortion tocapture a heavy metal may decrease.

FIG. 7 shows the concentration distribution of cobalt (Co) near thesurface of a pixel region (photoelectric converter PD) in a solid-stateimage sensor according to each of the example, Comparative Example 1,and Comparative Example 2 of the present invention. In FIG. 7, theabscissa indicates a depth from a first surface S1, and the ordinateindicates a cobalt concentration. The example is an example in whichoxygen peak concentration/carbon peak concentration=4% is obtained,Comparative Example 1 is an example in which carbon implantation is notperformed, and Comparative Example 2 is an example in which oxygen peakconcentration/carbon peak concentration=37% is obtained. The example,Comparative Example 1, and Comparative Example 2 are results obtained bymanufacturing the solid-state image sensors having the same structure onthe same condition from step S220 and evaluating the solid-state imagesensors.

It can be seen that the cobalt concentration near the surface of a pixelregion (photoelectric converter PD decreases by implanting carbon as theimpurity in a first semiconductor region 101 (single crystal siliconsubstrate). This indicates that an impurity-containing portion 190provided in a deep portion of a semiconductor substrate SS getterscobalt near the surface of the pixel region (photoelectric converterPD). It is confirmed that by adopting a semiconductor substrate with alow oxygen concentration as in the example (oxygen peakconcentration/carbon peak concentration=4%), gettering of cobalt isperformed more effectively than in a case in which a semiconductorsubstrate with a high oxygen concentration is adopted as in ComparativeExample 2.

FIG. 8 shows the number of white defects in a solid-state image sensoraccording to each of the example, Comparative Example 4, ComparativeExample 5, and Comparative Example 6 of the present invention. InComparative Example 4, the solid-state image sensor is manufactured byusing a semiconductor substrate SS obtained by preparing a firstsemiconductor region 101 with an oxygen peak concentration exceeding3×10¹⁸ [atoms/cm³] and growing a second semiconductor region 102epitaxially without implanting an impurity (carbon). In ComparativeExample 5, the solid-state image sensor is manufactured by using asemiconductor substrate SS obtained by preparing a first semiconductorregion 101 with the same oxygen peak concentration as in the example(3×10¹⁸ [atoms/cm³] or less) and growing a second semiconductor region102 epitaxially without implanting an impurity (carbon). In ComparativeExample 6, the solid-state image sensor is manufactured by using asemiconductor substrate SS obtained by preparing a first semiconductorregion 101 with the same oxygen peak concentration as in ComparativeExample 4 and growing a second semiconductor region 102 epitaxiallyafter implanting an impurity (carbon).

If implantation of a gettering impurity is not performed, the number ofwhite defects increases by decreasing oxygen concentration (ComparativeExamples 4 and 5). It is considered that this is because the getteringeffect decreases by decreasing the oxygen precipitation defects asdescribed above. It can be seen that the number of white defectsdecreases by implanting the impurity as in Comparative Example 6. Then,it can be seen that the number of white defects further decreases bydecreasing the oxygen concentration in addition to implanting theimpurity as in the example.

A reduction in afterimage in a photoelectric converter PD will bedescribed. The afterimage in the photoelectric converter PD may becaused by emitting signal charges from a level formed by oxygen sometimeafter the signal charges are captured in the level. Oxygen that may thuscause the afterimage can be collected in an impurity-containing portion190 of the semiconductor substrate SS and fixed, making it possible tosuppress the afterimage in the photoelectric converter PD. Inparticular, diffusion of oxygen from the first semiconductor region 101to the second semiconductor region 102 can be suppressed in theimpurity-containing portion 190, making it possible to decrease anoxygen concentration in the second semiconductor region 102. From thisviewpoint, it can be said that an oxygen concentration in theimpurity-containing portion 190 is preferably higher to the extent thatit does not exceed 1/10 of a peak concentration of a group 14 elementother than silicon.

FIG. 9 shows the partial arrangement of a solid-state image sensor 100according to the second embodiment of the present invention. Mattersthat are not mentioned in the second embodiment can comply with thefirst embodiment. The solid-state image sensor 100 has a semiconductorsubstrate SS (silicon substrate) including a first semiconductor region101 and a second semiconductor region 102 arranged on the firstsemiconductor region 101. The first semiconductor region 101 includes animpurity-containing portion 190. The semiconductor substrate SS has afirst surface S1 and a second surface S2 which are surfaces on oppositesides. One of two surfaces of the second semiconductor region 102opposite to the first semiconductor region 101 forms the first surfaceS1 of the semiconductor substrate SS. One of two surfaces of the firstsemiconductor region 101 opposite to the second semiconductor region 102forms the second surface S2 of the semiconductor substrate SS. Aplurality of impurity regions whose conductivity types or impurityconcentrations are different from each other are provided in the secondsemiconductor region 102.

The first semiconductor region 101 is made of single crystal silicon,and can be formed by slicing a single crystal silicon ingot andpolishing the slice. The second semiconductor region 102 is made ofsingle crystal silicon, and can be formed by epitaxially growing asingle crystal silicon layer on the first semiconductor region 101.Since a crystal lattice can continue between the first semiconductorregion 101 and the second semiconductor region 102, it may be impossibleto observe a clear interface. The second semiconductor region 102includes a semiconductor region 102 b of the first conductivity type anda semiconductor region 102 c of the second conductivity type.

The impurity-containing portion 190 contains a group 14 element(impurity) other than silicon (Si) and oxygen (O). Note that the group14 element includes carbon (C), silicon (Si), germanium (Ge), tin (Sn),and lead (Pb). The first peak concentration as a peak concentration ofthe group 14 element other than silicon in the impurity-containingportion 190 can be 1×10¹⁸ [atoms/cm³] or more and 1×10²⁰ [atoms/cm³] orless. An oxygen peak concentration in the impurity-containing portion190 can be 1/1000 or more and 1/10 or less of the first peakconcentration (1×10¹⁸ [atoms/cm³] or more and 1×10²⁰ [atoms/cm³] orless). The solid-state image sensor 100 manufactured by using theabove-described semiconductor substrate SS is advantageous in reducingwhite spots.

A photoelectric converter PD is arranged in the semiconductor substrateSS of the solid-state image sensor 100. The impurity-containing portion190 is arranged in isolation from the photoelectric converter PD. Thephotoelectric converter PD is arranged between the impurity-containingportion 190 and the first surface S1. The impurity-containing portion190 can be arranged so as to form a layer parallel to the first surfaceS1.

The photoelectric converter PD includes an impurity region 104 of thefirst conductivity type capable of functioning as a charge accumulationregion. In the impurity region 104 of the first conductivity type,signal charges form the majority carrier. The photoelectric converter PDcan also include, between the impurity region 104 and the firstsemiconductor region 101, the impurity region 102 c of the secondconductivity type. The impurity region 102 c can include a plurality ofsemiconductor regions 201, 202, 203, 204, and 205 of the secondconductivity type. The photoelectric converter PD can include, under theimpurity region 104, the impurity region 102 b of the first conductivitytype arranged continuously from the impurity region 104. Theconcentration of the impurity of the first conductivity type in theimpurity region 104 is higher than the concentration of the impurity ofthe first conductivity type in the impurity region 102 b. The impurityregions 104, 102 b, and 102 c form the photoelectric converter PD.

Out of negative charges (electrons) and positive charges (holes)generated by photoelectric conversion of the photoelectric converter PD,charges of the same type as the majority carrier in the firstconductivity type are accumulated in the impurity region 104. Thephotoelectric converter PD can include an impurity region 105 having thesecond conductivity type and arranged on the upper side of the impurityregion 104, that is, between the impurity region 104 and the surface ofthe semiconductor substrate SS. The impurity region 105 functions toisolate the impurity region 104 from the surface of the semiconductorsubstrate SS. The photoelectric converter PD having a buried photodiodestructure is thus formed.

FIG. 10 shows the concentration of an impurity of the secondconductivity type (p type here), the concentration of oxygen, and theconcentration of an impurity (carbon) taken along a line A-A′ in FIG. 9.A depth indicates a depth from the first surface S1 of the semiconductorsubstrate SS. C1 indicates a peak of an impurity of the secondconductivity type in the semiconductor region 201. C3 indicates a peakof the impurity of the second conductivity type in the semiconductorregion 202. C4 indicates a peak of the impurity of the secondconductivity type in the semiconductor region 203. C5 indicates a peakof the impurity of the second conductivity type in the semiconductorregion 204. C2 indicates a peak of the impurity of the secondconductivity type in the semiconductor region 205. A depth where acarbon concentration has a peak and a depth where an oxygenconcentration indicates a peak are positioned within the depth range ofthe impurity-containing portion 190. The semiconductor substrate SS hasan oxygen concentration of 2×10¹⁷ [atoms/cm³] or less when at least adepth from the first surface S1 falls within a range of 0 to 15 μm. Inan example shown in FIG. 10, the oxygen concentration has a peak of2×10¹⁸ [atoms/cm³] or more at a position deeper than a depth where theconcentration of the impurity of the second conductivity type has thepeak C2.

A solid-state image sensor 100 and a method of manufacturing the sameaccording to the third embodiment of the present invention will bedescribed with reference to FIGS. 11 and 12. Matters that are notmentioned in the third embodiment can comply with the first embodiment.In the third embodiment, an impurity-containing portion 190 is formed byion implantation after an epitaxial layer serving as a secondsemiconductor region 102 is formed.

First, in step S300, a single crystal silicon substrate as a firstsemiconductor region 101 is prepared by mirror-polishing and cleaning awafer that is sliced from a single crystal silicon ingot pulled by anMCZ method. Then, in step S310, the second semiconductor region 102(epitaxial layer) is formed on the first semiconductor region 101 byepitaxial growth. Consequently, a semiconductor substrate SS thatincludes the second semiconductor region 102 is formed on the firstsemiconductor region 101. Then, in step S320, an ion implantation mask Mis formed on the second semiconductor region 102. Note that the mask Mcan use, for example, a mask made of an organic material such as aphotoresist mask. It is preferable, however, that a mask made of aninorganic material such as a metal, ceramics, or glass is used becauseit can endure a high implantation energy. Although the mask M maycontact the semiconductor substrate SS, it is preferably separated fromthe semiconductor substrate SS especially when the mask made of theinorganic material is used. Then, in step S330, an impurity (a group 14element except for silicon, for example, carbon or germanium) isimplanted in the second semiconductor region 102 via the opening of themask M, forming the impurity-containing portion 190. The opening of themask M is formed such that the impurity (the group 14 element except forsilicon) is implanted in a region different from a region PD′ where aphotoelectric converter PD is to be formed.

Subsequently, in step S340, an element isolation portion 110, impurityregions 103, 108, and 109, the photoelectric converter PD, impurityregions 111, 112, and 113, and the like are formed in the semiconductorsubstrate SS. Then, in step S350, gate electrodes 114 and 115, gateinsulating films 116 and 117, insulating layers 118 and 123, the wiringlayers 120 and 122, a contact plug 119, a via plug 121, a color filterlayer 124, a microlens 125, and the like are formed on the semiconductorsubstrate SS.

The impurity-containing portion 190 can be arranged at a position apartfrom a light receiving surface (a portion of a first surface S1 of thesemiconductor substrate SS positioned above the photoelectric converterPD) and may be arranged at, for example, the same depth as thephotoelectric converter PD. The impurity-containing portion 190 may beformed by implanting an impurity (the group 14 element except forsilicon, for example, carbon) selectively under the region PD′.

FIG. 13 is a block diagram for explaining an example of the arrangementof a camera to which the solid-state image sensor 100 described in theabove example is applied. The camera includes, for example, a signalprocessor 200, a CPU 300 (or a processor), an operation unit 400, and anoptical system 500 in addition to the solid-state image sensor 100. Thecamera can further include a display unit 600 configured to display astill image or a moving image to the user, and a memory 700 configuredto store the data. The solid-state image sensor 100 generates image dataformed from a digital signal based on light that has passed through theoptical system 500. The image data undergoes predetermined imageprocessing by the signal processor 200 and is output to the display unit600 or the memory 700. In addition, the CPU 300 can change the settinginformation of each unit or the control method of each unit based on animaging condition input by the user via the operation unit 400. Theconcept of the camera includes not only apparatuses mainly aiming atshooting but also apparatuses (for example, a personal computer or aportable terminal) having an auxiliary shooting function.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2016-238781, filed Dec. 8, 2016, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A photoelectric conversion device that includes asilicon substrate, wherein the silicon substrate includes a firstportion configured to perform photoelectric conversion, and a secondportion containing carbon, the second portion being arranged fartherapart from a light receiving surface of the silicon substrate than thefirst portion, wherein a carbon peak concentration in the second portionis 1×10¹⁸ [atoms/cm³] to 1×10²⁰ [atoms/cm³], and wherein an oxygen peakconcentration in the second portion is 1/1000 to 1/10 of the carbon peakconcentration.
 2. The device according to claim 1, wherein the firstportion is arranged between the second portion and the light receivingsurface in a direction perpendicular to the light receiving surface. 3.The device according to claim 1, wherein the first portion is arrangedin a region in which a carbon concentration is less than an oxygenconcentration.
 4. The device according to claim 1, wherein a position atwhich the silicon substrate indicates the carbon peak concentration isarranged such that a distance from the light receiving surface is 3 μmto 20 μm.
 5. The device according to claim 1, wherein the second portionincludes a first region with a carbon concentration of not less than1×10¹⁸ [atoms/cm³], and a dimension of the first region in a directionperpendicular to the light receiving surface is not more than 3 μm. 6.The device according to claim 1, wherein the second portion includes asecond region with a carbon concentration of not less than 1×10¹⁹[atoms/cm³], and an oxygen concentration in the second region is notmore than 3×10¹⁸ [atoms/cm³].
 7. The device according to claim 1,wherein the second portion includes a third region with a carbonconcentration of 1×10¹⁸ [atoms/cm³] to 1×10¹⁹ [atoms/cm³], and an oxygenconcentration in the third region is not more than 1×10¹⁸ [atoms/cm³].8. The device according to claim 1, further comprising a peripheralcircuit portion configured to read out a signal from a pixel thatincludes the first portion, wherein the peripheral circuit portionincludes a transistor that includes a silicide region, and wherein thesilicide region contains at least one of nickel and cobalt.
 9. Thedevice according to claim 1, wherein the silicon substrate is providedwith an element isolation portion formed by an insulator having an STIstructure.
 10. The device according to claim 1, wherein the firstportion includes: an n-type first impurity region; and a p-type secondimpurity region positioned between the first impurity region and thesecond portion, and wherein an n-type impurity region is providedbetween the second impurity region and the second portion.
 11. A cameracomprising: a photoelectric conversion device defined in claim 1; and aprocessor configured to process image data from the photoelectricconversion device.
 12. The device according to claim 1, wherein thesilicon substrate indicates the carbon peak concentration at a firstdepth in the silicon substrate, and indicates the oxygen peakconcentration at a second depth in the silicon substrate, and whereinthe first depth is about the same as the second depth.
 13. A method ofmanufacturing a semiconductor substrate, the method comprising:preparing a silicon plate, which includes an oxygen-containing portionwith an oxygen concentration of more than 2×10¹⁶ [atoms/cm³] to lessthan 8×10¹⁷ [atoms/cm³] and a carbon-containing portion with an oxygenconcentration being not more than 3×10¹⁸ [atoms/cm³]; and forming asilicon layer on the silicon plate so that the carbon-containing portionis arranged between the oxygen-containing portion and the silicon layer,wherein the semiconductor substrate contains silicon of the siliconplate and silicon of the silicon layer, wherein a carbon peakconcentration in the semiconductor substrate is 1×10¹⁸ [atoms/cm³] to1×10²⁰ [atoms/cm³], and wherein an oxygen peak concentration in thesemiconductor substrate is 1/1000 to 1/10 of the carbon peakconcentration.
 14. The method according to claim 13, wherein thepreparing of the silicon plate includes implanting carbon in a siliconwafer with an oxygen concentration of 2×10¹⁶ [atoms/cm³] to less than8×10¹⁷ [atoms/cm³], and wherein the silicon plate contains silicon ofthe silicon wafer.
 15. The method according to claim 14, wherein theimplanting the carbon is performed by accelerating and implanting carbonions with an acceleration energy of 10 KeV to 200 KeV.
 16. The methodaccording to claim 14, wherein the implanting the carbon is performedsuch that a dose of the carbon is more than 1×10¹⁴ [atoms/cm²] to lessthan 5×10¹⁵ [atoms/cm²].
 17. The method according to claim 14, whereinin the implanting carbon, a mask having an opening is used, and carbonis implanted via the opening.
 18. The method according to claim 13,wherein the preparing of the silicon plate includes forming a singlecrystal silicon ingot by an MCZ method, and forming a silicon wafer byslicing the single crystal silicon ingot, and wherein the silicon platecontains silicon of the silicon wafer.
 19. A method of manufacturing aphotoelectric conversion device, the method comprising: preparing asilicon substrate, the silicon substrate including a first semiconductorregion and a second semiconductor region arranged on the firstsemiconductor region; and forming a photoelectric converter in thesecond semiconductor region, wherein a carbon peak concentration in thefirst semiconductor region is 1×10¹⁸ [atoms/cm³] to 1×10²⁰ [atoms/cm³],and wherein an oxygen peak concentration in the first semiconductorregion is 1/1000 to 1/10 of the carbon peak concentration.
 20. Themethod according to claim 19, wherein the first semiconductor regionincludes an oxygen-containing portion with an oxygen concentration ofmore than 2×10¹⁶ [atoms/cm³] to less than 8×10¹⁷ [atoms/cm³].
 21. Themethod according to claim 20, further comprising forming, in the secondsemiconductor region, a transistor of a peripheral circuit portionconfigured to read out a signal from a pixel that includes thephotoelectric converter, wherein the transistor includes a silicideregion, and wherein the silicide region contains at least one of nickeland cobalt.
 22. A photoelectric conversion device comprising: a siliconsubstrate in which a photoelectric converter is arranged; and a gateelectrode of a transistor arranged on a surface of the siliconsubstrate, wherein a carbon concentration at a position in siliconsubstrate, the position being farther apart from the surface of thesilicon substrate than the photoelectric converter, is 1×10¹⁸[atoms/cm³] to 1×10²⁰ [atoms/cm³], and wherein an oxygen concentrationat the position is 1/1000 to 1/10 of the carbon concentration at theposition.
 23. The device according to claim 22, wherein the carbonconcentration at the position is not less than 1×10¹⁹ [atoms/cm³]. 24.The device according to claim 23, wherein the carbon concentration atthe position is not less than 1×10¹⁸ [atoms/cm³].
 25. The deviceaccording to claim 22, wherein the silicon substrate includes a regionwith an oxygen concentration of more than 2×10¹⁶ [atoms/cm³] to lessthan 8×10¹⁷ [atoms/cm³], and wherein the region is arranged fartherapart from the surface of the silicon substrate than the position. 26.The device according to claim 25, wherein the oxygen concentration ofthe region is less than 2×10¹⁷ [atoms/cm³].
 27. The device according toclaim 25, wherein the oxygen concentration of the region is more than acarbon concentration of the region.
 28. The device according to claim22, wherein the transistor includes a silicide region, which contains atleast one of nickel and cobalt.
 29. The device according to claim 22,wherein a distance between the surface and the position is 6 μm to 12μm.
 30. A camera comprising: a photoelectric conversion device definedin claim 22; and a processor configured to process image data from thephotoelectric conversion device.